Given a Binary Search Tree and two nodes p and q, find their Lowest Common Ancestor (LCA).
The LCA is the deepest node that has both p and q as descendants (a node can be its own descendant).
With this BST and p = 2, q = 8:
6
/ \
2 8
/ \ / \
0 4 7 9
The LCA is 6. Both 2 and 8 are descendants of 6, and no deeper node contains both.
If p = 2 and q = 4, the LCA is 2 (since 2 is an ancestor of 4, and a node can be its own ancestor).
Constraints: All values are unique. p and q exist in the tree.